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Abstract

Proof of concept results are presented towards an in situ bimodal proximity sensor for neurovascular bundle detection during dental implant surgery using combined near infrared absorption (NIR) and optical coherence tomography (OCT) techniques. These modalities are shown to have different sensitivity to the proximity of optical contrast from neurovascular bundles. NIR AC and DC signals from the pulsing of an artery enable qualitative ranging of the bundle in the millimeter range, with best sensitivity around 0.5-3mm distance in a custom phantom setup. OCT provides structural mapping of the neurovascular bundle at sub-millimeter distances in an ex vivo human jaw bone. Combining the two techniques suggests a novel ranging system for the surgeon that could be implemented in a “smart drill.” The proximity to the neurovascular bundle can be tracked in real time in the range of a few millimeters with NIR signals, after which higher resolution imaging OCT to provide finer ranging in the sub-millimeter distances.

NIR measurement setup for simulating a pulsing artery embedded in bone phantom, using a cardiac pulsatile pump, silicone tubes and liquid tissue-simulating phantoms. A fibered laser source sends light to the sample and a fiber probe with multiple source-detector separation options (collection optical fibers) collects the light and sends it to the customized detector, whose signal is recorded on an oscilloscope.

Fiber optic probe for NIR experiments. The fibers are each 600μm core diameter and fixed next to each other with a center-to-center distances of approximately 650μm. Typically fiber 1 is used as the source channel, and one of the remaining fibers can be used as the detection channel.

A sample oscilloscope screenshot of the raw pulse signal (yellow, CH1), and reference signal from the pressure gauge (cyan, CH2), showing the cardiac-simulated pressure generated by the pump and detected by the probe. Horizontal axis: time, 500ms per division.

Picture of one human mandible sample used in the OCT measurements (shown with neurovascular bundle removed). The OCT measurement was taken as indicated just above the mandibular canal (the hole under the black arrow) where the IAN neurovascular bundle is located. The bone was filed into a taper shape to give varying thickness of bone tissue above the canal.

An SS-OCT B-scan of the tapered jaw bone, with the tapered edge placed horizontally at the top of the image so that the mandibular canal and IAN descend in depth from left to right. The position of the first surface of the canal containing the IAN neurovascular bundle is indicated by the white arrows.